1. Field of the Invention
The present invention relates to a communications apparatus designed to be connected to a network, and more particularly, to a communications apparatus such as a router accommodating a plurality of different circuits and having a switching function. More particularly still, the present invention relates to a method for queuing inside a router, and to back pressure control and related technique that is one type of traffic control.
2. Description of Related Art
Conventionally, a relay apparatus called a router is used to connect a plurality of networks and to route and relay data. The router converts the network protocol and address and establishes a data relay path.
FIG. 1 shows an example of a conventional network composition. Routers 10-13 connect different networks. For example, the router 10 connects the Sonet/SDH ADM (Sonet/Synchronous Digital Hierarchy Add-Drop Multiplexer) 14, ATM (Asynchronous Transfer Mode) dedicated line service network 15, OC-48DWDM (Dense Wavelength Division Multiplexing) network 16, and OC 48cDWDM network 17. In other words, the router 10 accommodates circuits of different transmission speeds (in other words, different interfaces). Similarly, the other routers 11-13 also connect different networks to each other and relay data.
This type of router relays packets of different sizes (lengths). That is, the packets it handles are of variable length. Additionally, when one circuit is congested, the router performs back pressure control to prevent the influx of packets to that circuit and thus prevent packet loss on an ethernet port unit basis (in other words, a circuit unit basis). For example, in case one port is congested, the router performs back pressure control on the circuit connected to that port. For example, in a case in which the router is equipped with a buffer for every port, the router restricts the influx of packets to the congested buffer.
However, one drawback of the conventional router is that it cannot accommodate different networks efficiently and relay data efficiently. More specifically, the conventional router has the following drawbacks.
First, internal control becomes extremely complicated when the conventional router attempts to relay different networks in order to relay variable length packets, and it is extremely difficult to perform QoS (Quality of Service) control for all the different transmission speeds involved. In this case, back pressure control is exerted on an ethernet port unit basis, which means that efficient back pressure control is not always exerted over packet processing at different transmission speeds such as ATM (Asynchronous Transfer Mode) and POS (Packet Over Switch). Accordingly, the conventional router cannot perform QoS control effectively and efficiently for different transmission speeds.
Second, because the conventional router has a buffer for every output port, the buffer cannot be used efficiently. For example, in a case in which one output port is congested and another output port is not, the overall router buffer utilization efficiency is low. In order to solve this problem it is possible to aggregate the output circuits (ports) and provide a single common buffer. However, when the router receives a request for back pressure control of a given output circuit, the router continues to be influenced by the backlog until data is received to the effect that the output circuit is not congested, creating a blocking situation in which data cannot be output.
Third, for purposes of reliability and conservative operation, the typical router is a multiplex router. In such a multiplexed router, when configured so as to commence control under backlog from either a working system or a passive system, there is a possibility that, depending on the latency and router state, the working system and passive system may fail. Accordingly, when switching from the working system to the passive system, depending on the back pressure controlled state and the buffering state, there is the possibility that a doubling up or a skipping of data may occur. Additionally, when a failure has occurred in the passive system and a backlog occurs, the working system is affected despite the breakdown in the passive system.
Fourth, ATM circuits have standards for data jitter and delay. In order to uphold those standards, ideally back pressure control would not be undertaken at all. However, in terms of effective utilization of the buffer, performing back pressure control is desirable. However, whenever back pressure control must be performed frequently it is impossible to satisfy data jitter and delay standards.